Automatic synchronous transmissions, of the countershaft design, have been used in different types of motor vehicles for a considerable time. For example, DE 102 42 823 A1 discloses an automatic transmission of a countershaft design in which an input shaft and an output shaft are arranged coaxially and parallel to a countershaft. The drive torque of the input can be optionally transferable, via a fixed gear pair on the input shaft and the countershaft, as well as via gear-specific, idler-gear fixed gear pairs of the countershaft to the output shaft, or conducted, via a direct mechanical coupling, from the input shaft and the output shaft to the former.
This known transmission also has coupling devices by means of which the idler gears can be drivingly coupled to the output shaft in order carry out a concrete transmission shifting operation. A transmission brake is also present for the purpose of synchronizing the speeds by means of which the transmission gearwheels can be decelerated in order to perform up-shifting operations. In order to reduce manufacturing costs and optimize installation space, this transmission brake is designed as part of the coupling device as a whole, while the other coupling devices are independent of the braking and synchronization devices.
A disadvantage of this automatic synchronous transmission is that when engaging a starting gear, when the vehicle is at a standstill or at low speed, there can be unwanted acceleration. This is the case when the starting clutch was engaged before engaging the gear, and the vehicle is not braked against unwanted movement. The reason for this is that the speed of the countershaft must be decelerated to a speed near zero in order to engage a starting gear (the vehicle is at a standstill, so therefore the transmission output is also at a standstill). For this purpose, the kinetic energy of the countershaft is diminished via the transmission. However, this results in part of the kinetic energy of the countershaft leading to an acceleration of the transmission output. That leads to an unwanted acceleration of the vehicle.
Against this background, the task of the invention is to provide a method and a device for operating an automatically synchronized transmission, of a countershaft design, in which there is no unwanted acceleration of the vehicle when a starting gear is engaged and the vehicle is at a standstill.